The method and apparatus of the present invention is motivated by the need for safe and effective Deactivation and Decommissioning (D&D) of ventilation ductwork, enclosures, and buildings containing dust, lint, and particulates that prevents the release of radionuclides and other dangerous or unsafe particulate contaminants. Numerous examples exist of using fogging techniques to fix radionuclide contamination for a variety of situations. However, these techniques tend to work only on thin layers of contamination, and historically, they have not been effective on large particles such as lint and dust trapped in ducts of interest. The invention described herein is novel and has not been attempted before.
Contamination control is crucial during D&D activities, as well as during modifications to existing systems. In several of the older processing facilities, it is well known that contamination, in some cases substantial contamination, is present throughout the exhaust ductwork due to the years of processing in glove boxes, etc. A critical area of concern during the decommissioning of radioactive facilities is the prevention of the spread of radiological contamination. This is more serious for areas where large accumulations of radioactive dust and lint are present that have the potential to “go airborne”, such as disposal site exhumation, laundry facilities, exhaust ventilation ducting and exhaust stacks. In a recent demolition of large ventilation ducting (about 10-ft cross section and 100-ft long) at the US Department of Energy's (DOE's) Brookhaven National Laboratory, a spray coating was applied to the duct from inside using a painter dressed in anti-contamination clothing and an airline respirator system.
A different scenario at the U.S. DOE's Idaho National Laboratory (INL) required that a backhoe operator be placed in a contamination proof, positive pressure cab to prevent airborne contamination. In the case of the Idaho example, the required change of operators (required every two hours due to limitations using positive pressure system), and the anti-contamination clothing alone amounted to thousands of dollars per day.
In another case at the Idaho Site, there were significant accumulations of lint at a radioactive laundry. Traditional methods of capturing the lint prior to decommissioning, like simple glycerin fogging methods, were not successful, because they did not penetrate and bind the lint (see FIG. 1). The duct 1 shown in FIG. 1 is contaminated with lint 2, 3, 4, 5 attached to the wall and needs to remain attached to the wall 1 of the duct 1 during decommissioning. Some of the lint is large 4, 5 and hangs from the walls. The estimated loss of productivity typically exceeds fifty percent on most of the projects when respiratory protection required. These conditions exist in DOE Facilities where airborne contamination mandates the use of costly contamination controls and significantly reduces worker productivity.
There have been attempts of applying a coating in the past. However, these attempts have not been successful in penetrating and adhering contaminated lint and dust to the ductwork. As a result, that contamination was not fixed and ultimately became airborne when it was disturbed. Improved capture coating formulation will penetrate large amounts of lint and dust present in the ductwork and make the lint and dust, and any radioactive contaminants trapped in the lint and dust, adhere to the substrate material to allow ducting to be removed and compacted without spreading contamination. Since a “fog” acts as a gas, it can be introduced into the ductwork at a very low pressure and low velocity and will travel throughout the ducting with only an entry and exit point. The fogging has a number of operational advantages over spraying, which requires a spray hose and nozzle to be inserted and moved along the ducting. The spraying method has the potential of disturbing the contamination during the spraying itself, which depends on the pressure and velocity at which it is implemented.
The current glycerin-based capture coatings are formulated to remain tacky for prolonged periods, allowing any re-suspended contaminant particles to become captured when they contact the surface. However, this coating is formulated only to remove airborne contaminants and will not soak into the lint and dust deposited on the ducting surface. By formulating a new capture coating (containing surfactants and other components) and ensuring the delivery method supplies adequate amounts of the coating, as well as providing adequate coverage of the entire surface area of the ductwork, this new capture coating will reduce or eliminate the requirement for glovebags and extensive contamination control during cutting and removal of ductwork. This control is achieved by fixing the contaminants to the surface of the duct so that the danger of creating airborne contaminants is reduced.
There are a number of technologies that have been used for this application with limited success. They are:                Spraying the fixative into the ductwork Although the fixative could be sprayed into the ductwork, rather than being applied in a fog through the ventilation system, there are several disadvantages with this approach. This method of application might require access to the ductwork in several different locations to obtain full coverage. This would require inserting the spray nozzle/wand and then applying the fixative to the local area. In some instances, the ductwork could be highly contaminated and even though physical access is available, it may not be allowed due to the radioactive field present. Therefore, in those instances of high contamination, the spray method may not be allowed. Once the nozzle/wand is inserted into the ductwork, the potential spread of contamination exists during the removal of the nozzle/wand. This would also require bagging the equipment during removal, and continuous monitoring during the application to assure workers are not contaminated.        Vacuuming/cleaning the ductwork prior to removal. Although this method is used widely in both the residential and commercial sector, it is considered unacceptable for most radionuclide applications. The main reason is because the material that is removed during the vacuuming/cleaning is contaminated. Therefore, a new waste stream has been generated and now must be disposed of properly. Furthermore, a risk of contamination to workers due to radiation exposure and also the potential for the spread of that contamination outside the ductwork exists during the vacuuming/cleaning. In addition, depending on the amount of contamination and the type of contamination, criticality could be an issue due to the method of capture of the contamination and the configuration of that capture device.        Wetting down the inside of the ductwork with water. Again, although this method is widely used in the D&D of facilities to help reduce the potential airborne constituents during massive demolition, this method could also result in an additional waste stream, and the potential for increased airborne contamination during the application of the water depending on the quantity and method of the water applied. Also, depending on what contaminants are present in the ductwork, introducing water to some of those contaminants could result in severe chemical reactions. Those reactions could include an over-pressurization of the system, explosion, or fire. Furthermore, for those instances where a modification is being made to the system, rather than demolition of the entire system, the addition of water into the ductwork is unacceptable due to the numerous adverse affects of that water into the ventilation system and components (e.g., HEPA filter wetting).        A combination technique involving fogging and coating of contaminants. A combination technique was used successfully at the East Tennessee Industrial Park on the decommissioning project in Irwin, Tenn. Fogging was used to reduce contamination and spraying was used to coat and lock the contaminant in place.        
The invention proposed herein addresses the deficiencies of and greatly enhances the performance of fogging methods in terms of reducing or eliminating contamination and increasing worker safety, particularly where capture coatings are to be fogged into dusty areas and ductwork. While testing has been performed to prevent the generation of airborne radioactive contamination, none dealt directly with the problem of penetrating significant quantities of dust and lint, and then capturing them in one step. A fog behaves similar to a gas. As a consequence, it can be introduced into ductwork at low pressure and low velocity. The approach was to use a more sophisticated solution containing a sticky base and a surfactant to increase the penetration and capture of dust and lint. A wide range of laboratory tests were conducted with the following criteria to improve the fogging fixative:                ability to produce a fog,        ability to penetrate a consistent simulated lint coupon,        ability to maintain a sticky surface over a period of hours,        ability to wet the surface of the lint/dust, and        ability to prevent dust generation after dry.        
The fogging technology has the potential to be applied across a variety of industries.                DOE Decontamination. Several DOE site facilities throughout the United States that supported the Cold War and other research type missions are currently going through the decontamination process. As was the case for the commercial applications, the solution developed can be applied into the ventilation system, pipes, and rooms to fix contamination that has accumulated over years of operation at these facilities. The contamination can be both nuclear, as well as chemical. In either case, airborne release that occurs when the contamination is disturbed is a concern. Again, since the fogging method of this invention can be done remotely, the exposure of the worker to the contamination is eliminated. Also, since the key to the fixative solution described herein is the capability to penetrate and then fix the contamination at a very low pressure and velocity, this separates it from the other type fogging processes currently being used.        Commercial nuclear industry. Some commercial nuclear plants have been shut down and de-commissioned. During the decommissioning phase, contamination control is crucial. Whether it be dismantling of contaminated ductwork, piping, or rooms, the control of airborne contamination is necessary to assure the spread of the contamination does not occur. In almost all instances today, workers manually apply some type of fixative in an attempt to control the spread of contamination. In some cases, this works very successfully; however, since the application is being applied manually, exposure risks are a concern from a safety standpoint. Also, in some instances, the fixative does not penetrate the contamination completely. As a result, once the contamination is disturbed some of that contamination still becomes airborne. Without having some type of means to penetrate the contamination and to ensure it is fixed to the material, the spread of that contamination is inevitable. With the new fogging method of this invention, having the capability to penetrate the contamination allows the dismantling of the facility in a quicker and safer manner. In addition, the new fogging solution described herein can be applied remotely without the need for manual application, eliminating the exposure safety concern.        Chemical plant demolition. There are several chemical plants throughout the world generating chemicals either as a by-product during the operation of the facility, or as the main product of production. In either case, when the plants are shut down, for any reason, demolition of the facilities is necessary. As is the case in all these examples, fixing the chemical agents to the ductwork, pipe and walls becomes crucial in eliminating the potential airborne release of these chemical agents once they are disturbed. In some instances, the buildup during the years of operation of these facilities could be significant. As a result, the capability to penetrate into the agent to ensure it is fixed and to perform this remotely without jeopardizing exposure concerns is a must. The fixative solutions described herein have this capability and could prove to be a key contributor in eliminating airborne releases in many different applications.        Asbestos abatement One of the major concerns with asbestos is the small fibers becoming airborne and entering the lungs. The new fogging described herein could be applied into a room where asbestos is located. The solution would penetrate into the surface of the asbestos and would not allow the fibers to become airborne. Thus, creating a shell type configuration preventing the release of the asbestos fibers and allowing the removal of the asbestos under safer conditions. In some instances, paint is applied to the asbestos to create a similar type of configuration. However, the current method of application of the paint still requires workers to be in the room during the application, whether it be sprayed on to the surface of the asbestos, or applied by hand. Either way, manned entry is necessary. With the fixative solutions described herein, a fog could be applied to the room, even focusing the application to the specific area remotely. Again, this limits the exposure concern.        National Security Building Decontamination Support. In the event of a terrorist act, where an agent of some type (chemical or radiological) is introduced into a building through the ventilation system, the fogging solution described herein could be applied into the building ventilation system, to penetrate, capture and fix the agent to the surface. At that time, decontamination efforts can commence in a safer environment without the concern of further spread of the agent through the building or outside of the building. Thus, this eliminates the exposure risk to the workers performing the decontamination, and also, to the general public near the building. In addition, if the agent introduced did spread throughout the building and the building was a complete loss, the solution could be applied through the ventilation system into the building also penetrating, capturing and fixing the agent to the building surfaces. This would eliminate any airborne contamination from spreading during the building demolition.        Naval Decommissioning. Again, this technology can be used throughout the Naval decommissioning process, in the event various types of contamination has occurred, to fix contamination to the surface to allow for a safer and faster type of dismantling. Since it can be applied remotely at low pressures and velocities, it will eliminate the exposure of the worker and also the spread of contamination during the application of the solution.        
The proposed invention described herein, mainly using latex paint as one of the constituents of the aqueous fixative solution, while very simple, has not been used before. It will                result in a more efficient industrial process,        eliminate the need to pre-sweep or vacuum exhaust ducts, thus reducing waste,        minimize the potential spread of contamination,        minimize the need costly anti-contamination protective equipment for workers, and        increase worker productivity.        